Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.

Abstract

Basophils are increasingly recognized as playing important roles in the immune response toward helminths. In this study, we evaluated the role of basophils in vaccine-mediated protection against filariae, tissue-invasive parasitic nematodes responsible for diseases such as elephantiasis and river blindness. Protective immunity and immunological responses were assessed in BALB/c mice vaccinated with irradiated L3 stage larvae and depleted of basophils with weekly injections of anti-CD200R3 antibody. Depletion of basophils after administration of the vaccination regimen but before challenge infection did not alter protective immunity. In contrast, basophil depletion initiated prior to vaccination and continued after challenge infection significantly attenuated the protective effect conferred by vaccination. Vaccine-induced cellular immune responses to parasite antigen were substantially decreased in basophil-depleted mice, with significant decreases in CD4(+) T-cell production of IL-4, IL-5, IL-10, and IFN-γ. Interestingly, skin mast cell numbers, which increased significantly after vaccination with irradiated L3 larvae, were unchanged after vaccination in basophil-depleted mice. These findings demonstrate that basophils help establish the immune responses responsible for irradiated L3 vaccine protection.

Basophil depletion after vaccination with irradiated L3 larvae does not alter protection against L. sigmodontis challenge

A) Timeline of experimental protocol. Both vaccinated (Vacc) and vaccinated and basophil-depleted (Vacc+Depl) groups were vaccinated with three weekly subcutaneous injections of 25 irradiated L3s. Both of these groups, plus an unvaccinated control group (No Vacc) were challenged by subcutaneous injection of 40 L3 larvae on day 28 of the protocol, two weeks after the final vaccination. From days 16 (12 days prior to challenge) until study endpoint mice were administered weekly injections of Ba103 to deplete basophils (Vacc+Depl) or isotype control antibody (No Vacc and Vacc groups). B) Number of adult parasites recovered from thoracic cavity at study endpoint four weeks after challenge infection (*** p < 0.001).

A) Timeline of experimental protocol. Both vaccinated (Vacc) and vaccinated and basophil-depleted (Vacc+Depl) groups were vaccinated with three weekly subcutaneous injections of 25 irradiated L3s. Both of these groups, plus an unvaccinated control group (No Vacc) were challenged by subcutaneous injection of 40 L3 larvae on day 28 of the protocol, two weeks after the final vaccination. From days -2 (2 days prior to vaccination) until study endpoint mice were administered weekly injections of Ba103 to deplete basophils (Vacc+Depl) or isotype control antibody (No Vacc and Vacc groups). B) Number of adult worms recovered from thoracic cavity at study endpoint 4 weeks p.i. (** p < 0.01; NS no significant)

A) Timeline of experimental protocol. Both vaccinated (Vacc) and vaccinated and basophil-depleted (Vacc+Depl) groups were vaccinated with three weekly subcutaneous injections of 25 irradiated L3s. A control group of mice was not vaccinated (No Vacc). From days -2 (2 days prior to vaccination) to day 28 mice were administered weekly injections of Ba103 to deplete basophils (Vacc+Depl) or isotype control antibody (No Vacc and Vacc groups). No mice were challenged with infective L3 larvae in this study. B) Proliferation and C–F) cytokine production of splenic CD4+ T-cells in response to parasite antigen measured after 3 days of culture. (PI = proliferative index; * p < 0.5; ** p < 0.01; *** p < 0.001; NS not significant).